This paper examines the desorption and self-exchange dynamics of polyelectrolyte chains on an oppositely charged surface, in the limit of weak charge, such that the polymer is readily displaced by added ions. The model system adhering to this physically limiting behavior is poly[(dimethylamino)-ethyl methacrylate] [PDMAEMA] adsorbing on silica from aqueous solution at elevated pH. Desorption kinetics follow expectations: a single-exponential decay consistent with a first-order desorption model, with an activation energy for chain removal that adheres reasonably to the Muthukumar treatment and quantitatively to the Dobrynin-Rubinstein model. Self-exchange kinetics, however, present a surprise: They are quantitatively identical to desorption, with the exchange process being completely controlled by chain release from the surface. The single-exponential form for self-exchange is atypical, and the quantitative similarity with desorption suggests that, with weakly charged chains, approximately 3-5 segment-surface contacts make up a minimum dynamic unit for adhesion.